Drilling method and compositions therefor



May 21', 1968 J. L. PEKAREK ET AL.

A DRILLING METHOD AND CQMPQSITIONS THEREFOR Filed Dec. 27, 1965 Q %N\0000 v mm an vw x unh- //V YEA/T0195. JOSEPH L. PEK/I/PEK PAUL W SCH-4M5United States Patent O 3,384,189 DRILLING METHOD AND COMPOSITION I ITHEREFOR Joseph L. Pekarek and Paul. W. Schaub, Penn Hills Township,Allegheny County, Pa., assignors to Gulf Research & Development Company,Pittsburgh, Pa a corporation of Delaware Filed Dec. 27, 1965, Ser. No.516,400 8 Claims. (Cl. 175- 67) ABSTRACT OF THE DISCLOSURE Thisinvention relates to the drilling of wells and more particularly to animproved drilling process in which a stream of drilling liquidcontaining suspended ferrous abrasive is discharged at extremely highvelocities against the bottom of a borehole to drill through hardformations.

Improvements in conventional rotary drilling processes have greatlyincreased rates of drilling in soft formations and formations of mediumhardness. To a large extent, the improvenients have resulted from morepowerful equipment which allows the application of greater bit weightsto the cone or drag-type bits. One type of bit that is used widely todrill soft formations is referred to as the jet bit. It differs from theusual bit principally in directing the drilling mud against the bottomof the hole to clean the bottom of the hole rather than over the surfaceof the cutters to keep the cutters clean. The purpose of jet bits is toimprove the removal of cuttings broken from the formation by themechanical cutting elements of bits rather than to cut grooves in theforma tion being drilled; however, some penetration of soft formationsby the stream of drilling mud may be responsible for some of theincrease in drilling rate. Quick removal of the cuttings from the bottomof the hole reduces shielding of the bottom of the hole from the bit bythe cuttings and reduces regrinding of cuttings. The conventional jetbits have been ineffective in increasing the rate of drilling in hardformations.

Recently, a novel hydraulic jet drilling process which is effective inincreasing the rate of drilling of hard formations has been developed.In the hydraulic jet drilling process, an abrasive-laden liquid isdischarged at extremely high velocities against the bottom of the holeto cut the formation being drilled and remove cuttings from the hole. Inthe hydraulic jet drilling process, substantially all of the penetrationof the rock being drilled is accomplished by the abrasive-laden stream,and mechanical removal of rock from the bottom of the hole by cuttingelements on a bit is restricted to removal of ridges which may extendupward between grooves cut by the high velocity streamJIn the hydraulicjet drilling process, the weight applied to the nozzle head, referred tofor convenience as the bit, is approximately one-fourth, or less, of theweight applied in comparable conventional drilling methods. Hydraulicjet drilling in hard formations is substantially faster than drillingwith conventional rock bits but is still relatively slow compared todrilling in soft formations and further increases in hydraulic jetdrilling rates are desirable.

3,384,189 Patented May 21, 1968 The high velocity at which theabrasive-laclen stream passes through nozzles in the bit causes rapiderosion of the nozzle with a resultant increase in the diameterof theorifice in the nozzle. Because the rate of drilling is highly dependentupon the velocity at which the abrasiveladen stream strikes the bottomof the borehole, the reduced velocity resulting from enlargement of thenozzle orifice reduces the drilling rate and makes it necessary toreplace the bit. In deep wells, a substantial part of the rig time canbe used in making the round trips necessary to replace the bit. For thisreason, it is important to reduce the rate of erosion of the nozzles.

' -When the high velocity stream of abrasive-laden liquid strikes theformation being drilled, the abrasive, as well as the formation, issubjected to severe stresses. When sand is used as the abrasive in thedrilling, approximately one-half of the sand is broken up in a singlepass through the bit into fine particles unsuited for further use. Thelarge amounts of abrasive consumed causes the abrasive to be animportant part of the .cost of the hydraulic jet drilling process. It isdesirable to use an abrasive that breaks up only to a negligible extenton striking the bottom of the borehole and, hence, can be reused toreduce the abrasive requirements.

This invention resides in a method of drilling hard formations bydischarging a stream of a drilling liquid laden with ferrous abrasive atan extremely high velocity against the bottom of the borehole. We havefound that if the hardness of the ferrous abrasive exceeds about 55 onthe Rockwell C scale, an increased rate of cutting hard formations canbe attained with a reduced rate of erosion of the nozzles through whichthe abrasiveladen liquid is discharged against the bottom of the hole.The ferrous abrasive has a further advantage in hydraulic jet drillingprocesses resulting from the very low rate of break-up of the grit tosizes not effective in the hydraulic jet drilling process.

The single figure of the drawings is a diagrammatic illustration,partially in vertical section and partially expanded, of apparatus forhydraulic jet drilling of a well with a liquid having ferrous gritsuspended in it.

The ferrous abrasive used in the hydraulic jet drilling process of thisinvention may be either cast iron par-ticlcs or steel particles readilyavailable as commercial products used in the cleaning and treating ofmetal surfaces. Ferrous abrasives can be manufactured by blowing a highvelocity stream of air or steam against molten cast iron or steel toseparate globules of the metal. The globules are blown into water wherethey are chilled. The solidified particles are heat treated and gradedby size. Grit is prepared by crushing shot .and then heat treating thegranular particles and grading them according to size. Either angulargranular particles, referred to as grit, or rounded particles, referredto as shot can be used, but the shot is preferred because faster cuttingrates are obtained with shot. Ferrous abrasives having a Rockwell Chardness of at least about 55 give much higher drilling rates than sand.Ferrous abrasives of lower Rockwell C hardness have an advantage oversand of a much lower particle break-up rate, but have no advantage oversand in drilling rate. 'In some instances the softer ferrous abrasivesare even slower drilling than sand.

The ferrous particles used in this invention have a size in the range of7 to mesh. The drilling rate is faster with the particles of largersize, and it is desirable to use the largest particles that will passthrough the nozzles in the drill bit without plugging the nozzles. Innozzles having a minimum orifice of As-inch di ameter, ferrous abrasiveparticles having a size in the range of 16 to 50 mesh are preferred. Themaximum particle size of the abrasives is also limited by the ability ofthe high-pressure pumps to handle large particles. Particles of ferrousabrasives smaller than 40 mesh, such as 50-80 mesh, will cause drillingrates higher than can be obtained with 20 to 40 mesh sand and can beused. Because of the low rate of break-up of the ferrous abrasiveparticles and the effectiveness of particles as small as 80 mesh inhydraulic jet drilling processes, the ferrous abrasive can berecirculated for many cycles in the drilling operation.

The ferrous abrasive particles are suspended in a drilling liquid in aconcentration of /2 to 6 percent, preferably 1 to 4 percent by volume.Higher concentrations increase the amount of abrasive in the system andthe amount broken into fines without a corresponding increase indrilling rate. Lower concentrations of abrasive markedly reduce thedrilling rate. The drilling liquids used to suspend the ferrous abrasivemust have a relatively high gel strength and viscosity to remove theabrasive from the hole during the drilling operation and to preventsettling of the abrasive in the borehole when it is necessary to stopthe circulation of the drilling liquid. A suitable drilling liquid is aninvert emulsion of water and diesel oil containing 30 to 60 percent oil,with the oil in the continuous phase. A preferred drilling liquid is aninvert emulsion containing 40 to 50 percent diesel oil. The emulsion canbe stabilized by, for example, a sulfurized potassium soap of tall oilcontaining 5 percent sulfur. Other emulsifiers, such as polyhydricalcohol fatty acid esters, sulfated sperm oil soaps, and polyvalentmetal soaps f rosin acids can be used. The pH of the drilling liquid isadjusted to the range of 9 to 10 by the addition of alkaline materialsuch as caustic soda. Another suitable drilling liquid is an aqueousdispersion of bentonite containing 2 percent bentonite and 1 to 2percent Flosal, a fibrous asbestos material, Hydraulic jet drilling witha ferrous-abrasive-laden drilling liquid is not limited to the use ofany particular drilling liquid as long as the drilling liquid hasadequate gel strength and viscosity to give satisfactory suspension ofthe abrasive particles.

For purposes of illustration, a hydraulic jet drilling process will bedescribed in which 20 to 40 mesh particles of Indogrit, a cast irongranular material, manufactured by Industeel Company of Pittsburgh, Pa.,is suspended in an invert-emulsion drilling liquid containing 50 percentdiesel oil. The drilling liquid is delivered by high pressure pumps 10through a line 12 into the drill string 14 of a drilling rig 16 suitablyequipped to rotate the drill string in the borehole. The drilling liquidis pumped at a high rate downwardly through the drill pipe 14 anddischarged against the bottom 18 of the borehole 20 through nozzlesAa-inch in diameter in a bit 22 at the lower end of the drill pipe.Drill pipe 14 is rotated at a rate of at least r.p.m. during thedrilling. For effective drilling by the hydraulic jet drilling method,the drilling liquid must be discharged against the bottom of theborehole at an extremely high velocity of at least 500 feet per second,and preferably at least 600 feet per second, from nozzles having anoutlet A-inch to 1 /2 inches from the bottom of the borehole. Control ofthe spacing between the bottom of the hole and the nozzle outlets isobtained by means of stand-off bars on the bottom surface of the bit. Ina typical hydraulic jet drilling operation four pumps driven by motorssupplying a total of about 2,000 to 2,400 horsepower pump 450 to 600gallons per minute of the drilling liquid at a pressure of 5,000 p.s.i.to the drill pipe 14 for delivery to a bit head having a plurality ofnozzles, for example, 10 to nozzles /s-inch in diameter, having outletsapproximately /2-inch from the bottom of the borehole.

The drilling liquid and entrained cuttings pass upwardly through theborehole and are discharged the-refrom through line 24 and delivered toa shale shaker 4 26 in which the oversize cuttings are removed from thedrilling liquid. Ferrous-grit-laden drilling liquid is delivered throughline 28 to a bank of cyclone separators 30 in which abrasive particlesare separated from the liquid and delivered as an underfiow through line32. Overflow from separators 30 is delivered through line 34 to a secondbank 36 of separators in which further clean-up of ferrous-gridparticles from the drilling liquid is accomplished, and the ferrous-gritparticles separated in separators 36 are discharged as underflow throughline 38.

Overflow from separators 36 contains less than 0.2 percent particleslarger than 200 mesh and is delivered into a storage tank 40.Ferrous-grit-free drilling liquid is withdrawn from tank 40 through line42 and passed through another bank of cyclone separators 44 for removalof fine solid particles of 200 mesh size and smaller to reduce theconcentration of larger than 200 mesh particles to a trace and controlthe density of the drilling liquid. Clean drilling liquid from theseparators 44 is delivered through line 46 to the high pressure pumps10. Abrasive from lines 32 and 38 is mixed with the clean drillingliquid for recirculation in the well. Because of the low rate ofbreak-up of ferrous abrasives, removal of fines from all .of the liquidcirculated in the borehole is not required and drilling liquid may bedelivered fiom the shale shaker directly to pumps 10 through a suitablyvalved bypass line 48. Make-up abrasive is added to the system at shaleshaker 26 from a storage hopper 50.

The ferrous grit particles are effective in increasing the drilling rateover that which is obtained with other abrasive particles such as sand.A series of tests was made in which the abrasive-laden drilling liquidwas discharged from a single nozzle onto a block of hard black graniterotated in a horizontal plane about an axis 1 /2 inches from the bitaxis at a rate of about 30 r.p.m. The outlet of the nozzle wasmaintained /2-inch from the original rock surface during the tests. Thetests were made at a nozzle inlet pressure .of 5000 p.s.i. and adrilling liquid velocity of approximately 776 feet per second. Each testwas continued for a period of 20 seconds after which the depth of thecut was measured to give an indication of the drilling rate. Test runswere made on drilling liquids containing different concentrations of20-40 mesh cast iron and steel grit and shot of different Rockwell Chardness and with sand and alumina of the same size. The results arepresented in Table I.

TABLE I. Penetration of Black Granite, Inches Abrasive Concentration,

percent by Volume Run Material Rockwell G No. Hardness 1% 1%% 2% 4% 1Cast Iron Grit 35 25 3 .4 .5 (3%) 2--. Steel Grit 42-50 .25 .28 .32 5(5%) 3 Sand 7. 0 (M0115) 3 42 7 (3%) 4. Cast Iron Grit". 55-60 1. 5 1. 71.8 2. 5 5. Stool Grit. -65 1.1 1. 1. 8 2. 4 6. Cast Iron Sh 55-60 1. 82.05 2. 4 3. 5 7. Steel Sh0t 60435 1. 55 2. 1 2. 55 4. 3 8 A1203 9(Mohs) 6 0. 8 1. 0 1. 4

As shown by a comparison of Runs Nos. 6 and 7 with Run No. 3, drillingrates approximately five times the drilling rate with sand can beobtained wit-h ferrous shot having a Rockwell C hardness of at least 55.Ferrous grit of Rockwell C hardness greater than 55 gave drilling ratesthree times the drilling rate with sand. Softer ferrous abrasives gavedrilling rates actually lower than sand, as shown by Runs Nos. 1 and 2.Hardness is not the sole factor in hydraulic jet drilling. Both sand andA1 0 are harder than the iron or steel but result in slower drillingrates.

During the cutting test described above, the drilling liquid sampleswere caught, diluted, screened, dried, weighed, sieved, and reweighed.These data were then reduced to an average percentage of particleslarger than 40 mesh broken to smaller than 40 mesh. The results of theparticle break-up determinations are presented in Because of theextremely high velocities of the drilling liquid passing through thenozzles, erosion of the nozzles is an important factor in determiningthe feasibility of hydraulic jet drilling. A series of tests was run inwhich 20 to 40 mesh sand particles were pumped through a nozzle having a%-inch diameter inlet tapering down to a Aa-inch diameter orifice over adistance of 2 /2 inches and a straight section /2-inch long and Aa-inchin diameter extending from the orifice to the nozzle outlet. In thetest, suspensions of 20 to 40 mesh cast iron grit and of 20 to 40 meshsand were caused to fiow through the nozzle at rates giving a pressuredrop across the nozzle of 5000 psi. or more. The nozzles wereconstructed of two types of tungsten carbide. The results of the testsare presented in Table III.

TABLE III.-NOZZLE WEAR TESTS [Test duration: 6 hours] said bit having anozzle therein directed downwardly toward the bottomof the borehole,maintaining the nozzle outlet in the range of A-inch to 1 /2 inches fromthe bottom of the borehole of'the well, pumping a drilling liquid having/2 to 6 percent by'volume of ferrous abrasive suspended therein down thedrill stem, said ferrous abrasive particles having a' Rockwell Chardness of at least about 55, discharging the drilling liquid from thebit at a velocity of at least 500 feet per second against the bottom ofthe hole, and circulating the liquid up the borehole around the drillstring to carry cuttings from the borehole.

3. A method as set forth in claim 2 in which the abrasive particles areof a particle size in the range of 7 to SO mesh in the US. Sieve Series.

4. A method as set forth in claim 2 in which the ferrous abrasive isferrous shot having a Rockwell C hardness of at least and a particlesize in the range of 7 to 80 mesh in the US. Sieve Series.

'5. A method as set forth in claim 2 in which the ferrous abrasive issteel shot having a Rockwell C hardness of at least about 55 and aparticle size in the range of 7 to 80 mesh in the US. Sieve Series.

The results presented in Table III show that nozzle wear is much lowerwhen a ferrous abrasive, which had a Rockwell C hardness exceeding 55,is suspended in the drilling liquid than when the abrasive is sand inspite of the fact that the ferrous abrasive causes a much higherdrilling rate. Because the drilling rate is a measure of the ability ofthe drilling liquid to cut a hard surface, it is surprising that thenozzle erosion is less when iron grit is suspended in the drillingliquid than When sand is suspended in the drilling liquid. Contraryresults are obtained if tabular alumina is suspended in the drillingliquid. Although tabular alumina will give drilling rates exceedingthose obtained with sand but lower than those obtained with ferrousshot, nozzle erosion is so severe that tabular alumina cannot beeffectively used in hydraulic jet drilling operations.

Both cast iron and steel shot and grit having a Rockwell C hardness ofat least about 55 are highly advantageous in hydraulic jet drillingoperations in making possible high drilling rates through very hard rockformations. The high drilling rates can be obtained with a relativelylow rate of erosion of the nozzles through which the drilling liquid isdischarged against the bottom of the hole. Moreover, the low rate ofbreak-up of the ferrous grit particles allows their repeated use, andthereby greatly reduces the cost of the abrasive required in hydraulicjet drilling.

We claim:

1. In a hydraulic jet method of drilling a well in hard formations inwhich a drilling liquid is discharged at a velocity of at least 500 feetper second from a nozzle against the bottom of the borehole of the well,the outlet of said nozzle being in the range of A-inch to 1 /2 inchesfrom the bottom of the borehole, the improvement comprising suspendingin the drilling liquid ferrous abrasive particles in a concentration of/2 to 6 percent by volume, said ferrous abrasive particles having aRockwell C hardness of at least about 55.

2. A method of drilling a well in hard formations comprising rotating abit at the bottom of a drill string,

6. A method of drilling a well in hard formations comprising rotating adrill stem having a drill bit at its lower end in the borehole of thewell, pumping a drilling liquid having /2 to 6 percent by volume ferrousabrasive suspended therein down the drill stem and discharging theliquid from nozzles in the bit at a velocity of at least 500 feet persecond, said ferrous abrasive particles having a Rockwell C hardness ofat least about 55, the size of the abrasive particles being in the rangeof 7 to mesh, maintaining the outlet of the nozzles at a distance in therange of At-inch to 1 /2 inches from the bottom of the borehole,circulating the drilling liquid and cuttings upwardly through theborehole to the surface, separating cuttings and fine solid particlesfrom the drilling liquid, and recirculating drilling liquid containingthe ferrous abrasive in the well.

7. A method of drilling a well comprising rotating a bit mounted on thelower end of a drill string in the well at a rate of at least 5 r.p.m.,said bit having nozzles therein adapted to direct fluids against thebottom of the borehole, maintaining the outlets of the nozzles in thebit between Mt-inch and 1 /2 inches from the bottom of the borehole,pumping a liquid having /2 to 6 percent by volume ferrous abrasivesuspended therein down the drill stem and outwardly through the bit at arate adapted to give a nozzle outlet velocity of at least 500 feet persecond, said ferrous abrasive particles having a Rockwell C hardness ofat least about 55, circulating the liquid and entrained cuttingsupwardly through the well to the surface, removing cuttings and finelydivided solids from the drilling liquid, adding ferrous abrasive to thedrilling liquid to adjust the concentration of ferrous abrasive to 1 to6 percent by volume, and recycling the thusprepared drilling liquid downthe well for further drilling.

8. A drilling liquid for the hydraulic jet drilling of wells in hardformations comprising a liquid having suspended therein /2 to 6 percentby volume ferrous abrasive of a Rockwell C hardness of at least about55.

(References on following page) References Cited UNITED STATES PATENTSWuensch 17566 Boynton 175-67 Hays 17567 X Desbrow 175422 X Bergey 175-66Marwil 17566 Graham 17566 X Quick 17567 Bobo 17567 Stone 17566 Buck17566 CHARLES E. OCONNELL, Primary Examiner.

NILE C. BYERS, JR., Examiner.

